The UN's top court has ruled that Japan's whaling hunt in the Southern Ocean is not a scientific programme as Tokyo has always claimed.
''The court concludes that the special permits granted by Japan for the killing, taking and treating of whales in connection with JARPA II are not for purposes of scientific research,'' President Peter Tomka told the International Court of Justice in The Hague on Monday. The court ruled Tokyo should cease its whaling programme ''with immediate effect''.
The ICJ, by 12 votes to four, said Japan hadn't acted in compliance with its obligations under the international whaling convention.
Australia had asked the 16-judge panel to ban Japan's annual hunt on the basis it was not ''for purposes of scientific research'' as allowed under Article 8 of the 1946 International Convention for the Regulation of Whaling.
Canberra argued Tokyo was cloaking a commercial whaling operation ''in the lab coat of science'' despite agreeing to a 1980s ban on harpooning.
Japan, however, countered during a three-week hearing in mid-2013 that the ICJ didn't have the authority to decide what was, or wasn't, science.
It insisted lethal research was both lawful and necessary.
But the court on Monday dismissed Tokyo's argument.
New Zealand's Foreign Affairs Minister Murray McCully welcomed the decision, saying the court had ordered the whaling programme to cease.
"The ICJ decision sinks a giant harpoon into the legality of Japan's whaling programme: JARPA II," McCully said this evening.
"New Zealand has consistently opposed Japan's so-called 'scientific' whaling, which is a practice that is deeply offensive to many New Zealanders.''
McCully said he hoped Japan would "respect the Court's decision".
The court didn't accept Australia's argument that ''scientific research'' needed to have defined and achievable objectives, use appropriate methods, be properly peer reviewed, and avoid adverse events on the stocks being studied.
Instead it focused on whether Tokyo's program was ''for purposes of'' scientific research, however that was defined.
Judge Tomka said the key was whether ''the elements of the programme's design and implementation are reasonable in relation to its stated scientific objectives''.
Killing whales could be science and wasn't ''unreasonable per se'' in light of JARPA II's objectives, Judge Tomka said.
Furthermore, the fact whale meat was sold afterwards to fund future hunts didn't, on its own, mean the program fell outside the Article 8 exception.
But the court found there could be a greater reliance on non-lethal methods.
The court president said Tokyo should have analysed the feasibility of non-lethal methods when setting the quota size for taking whales.
He stated Japan couldn't take a larger catch than needed to meet its research objectives.
''There is no evidence that Japan has examined whether it would be feasible to combine a smaller lethal take, in particular of minke whales, and an increase in non-lethal sampling as a means to achieve JARPA II's research objectives.''
Tokyo was criticised for doubling its target to 850 minke whales each year after 2005 without first assessing the research effectiveness of its earlier programme, which had a much smaller sample size.
''This weakness in Japan's explanations for the decision to proceed with the JARPA II sample size prior to the final review of JARPA lends support to the view that those sample sizes and the launch date for JARPA II were not driven by strictly scientific considerations.''
The president said the fact the take of all species of whales was much lower than Japan's targets - often as a result of the activity of anti-whaling protests in the Southern Ocean - lent weight to Australia's argument sample size was relatively random.
''Japan has not acted in conformity with its obligations under ... the International Convention for the Regulation of Whaling,''Judge Tomka said.
- AAP, Fairfax NZ
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